Emergency services such as police and fire rescue often rely upon the local citizenry to alert emergency services of emergency situations. In order to do so, nearly every community in the United States has implemented an emergency call service, such as the well known 911 service. To be effective, an emergency call service needs to accomplish three goals. First, the emergency call service should recognize when someone dials the emergency number on any phone (even a pay phone when no coins have been supplied). Second, the emergency call service should route the call to the nearest available Public Safety Answering Point (PSAP) based on the call's originating location. Third, the emergency call service should notify the appropriate emergency response agency as quickly as possible so it can respond to the emergency.
While citizens reporting emergency situations could telephone a police or fire station directly through its individual local telephone number, it is more effective to provide citizens with a universal, short, easy to remember number that can be quickly dialed and directly connects to the nearest PSAP automatically. Most emergency call services in the U.S. and Canada utilize 911 as the short three digit emergency telephone number that automatically reaches a PSAP. As of 2006, 99 percent of the U.S. population had access to 911 services. Other countries have implemented the same or similar emergency call services for their citizenry. For example, the European Union has established 112 as the universal emergency number for all its member states. In most E.U. countries, 112 is already implemented and can be called toll-free from any telephone or any cellular telephone. For purposes of simplicity, emergency call service will be referred to herein as a 911 system.
Typically, there is no national 911 system. Rather, the answering points and corresponding dispatch services are locally established and maintained. In many locations in the U.S., for example, the 911 service is a joint effort between local governments and all phone companies active in the area. The cost of a 911 system is paid through local taxes and through a surcharge on the local citizenry's phone bill. Typically, the PSAP and corresponding emergency services are set up and maintained locally, usually by county, often in a joint effort between local government and any phone company active in the area. Once an emergency call is connected to the local PSAP, the appropriate local emergency services may be dispatched for fast response.
Within the conventional Public Switched Telephone Network (PSTN) system, emergency 911 calls are made through standard land line telephones operating on the PSTN. Because telephones in a conventional PSTN are stationary, various capabilities of a basic 911 system may be easily enabled. For example, Automatic Number Identification (ANI) may be implemented. As its name suggests, ANI automatically identifies the telephone number of the calling party. Coupled with Automatic Location Identification (ALI), the 911 system can automatically identify both the source and location of the calling telephone station. In this way, the location of the emergency situation may be determined without any verbal communication from the party making the 911 call. This is beneficial because in many times in emergency situations, callers are panicked or hurt and cannot verbally communicate the location or nature of the emergency. In addition, by automatically knowing the caller's location information, the 911 system may route the call to the nearest PSAP so as to dispatch the closest emergency response services to achieve the fastest response.
In addition, many phone companies and public safety agencies have collaborated to create Master Street Address Guides (MSAG) which are master maps that can match phone numbers, addresses and cross streets to their corresponding PSAP. When an emergency call is made, the 911 system network hub may use the MSAG to provide emergency response services with the fastest route to respond to the caller's location.
FIG. 1A illustrates the handling of a basic conventional 911 call. In a basic conventional 911 system, a caller 101 dials 9-1-1 (or the assigned emergency number). The PSTN switch automatically recognizes the 911 number and routes the call to a dedicated 9-1-1 switch 102 that sends the call to the designated PSAP 103 for the PSTN switch that first received the call.
The PSAP call-taker (also called an operator or dispatcher) asks what the emergency is, what the location is and for a call-back phone number. Depending on the emergency, the call-taker uses radio dispatch to alert police, fire and/or EMS to go to the scene.
FIG. 1B illustrates the handling of an enhanced conventional 911 call. In the enhanced 911 system, a caller 101 dials 911 (or the assigned emergency number). The PSTN switch recognizes the 911 number dialed and accesses the ANI to get the number of the station initiating the call and routes the call to the dedicated 9-1-1 switch 102 that acts as a hub for the local network. The network uses the telephone number of the initiating telephone station to get the address from the ALI and uses the address to determine the proper PSAP 103 destination from the MSAG 104 (this is sometimes called selective routing, because the switch uses dynamic data to determine where to send the 911 call instead of blindly routing it to a pre-determined PSAP). In most cases, this all takes a little over one second. The 911 call now carries the initiating call station phone number and address along with the caller's 101 voice data to the nearest available PSAP 103. This information is displayed on the call-taker's computer when he or she takes the 911 call.
Some PSAPs 103 simultaneously send the ANI/ALI data to the police computer dispatch network to allow for immediate access. If necessary, many PSAPs can transfer the call and its accompanying data to another PSAP.
While the 911 system is extremely effective when calls are initiated on conventional PSTN telephones, mobile device (e.g., cellular telephones) and Voice over Internet Protocol (VoIP) calls have posed new problems to 911 systems. For one, mobile devices and VoIP calls do not provide location information to the system. Thus, 911 calls may not be routed to the nearest PSAP. As of 2006, more than 8 million people in the United States use a mobile device as their primary phone. Public-safety agencies report that wireless calls make up anywhere from 30 to 50 percent of emergency service calls. To accommodate this transformation in the telephone usage, changes have been implemented in most 911 systems.
Until recently, when someone called emergency services from a mobile device, no information appeared on the call-taker's screen, even in enhanced emergency call service systems. Without this information, the emergency call wasn't always routed to the PSAP closest to the caller's location. Consequently, the emergency call could end up at any PSAP in the remote vicinity, depending on how the individual wireless provider servicing the particular mobile device had set up emergency call routing.
To address this problem, Congress has mandated that cellular service providers configure their systems and the mobile devices that they support so that the location of a caller can be determined when a 911 call is placed. Local 9-1-1 systems have been implementing changes to 9-1-1 to allow for greater wireless compatibility, and upgrades are still happening now. A number of methods are used to locate 911 callers. Many new mobile devices include a Global Positioning System (GPS) receiver within the mobile device's circuitry. Such mobile devices can provide location information to the cellular telephone system over a data link. Cellular systems can also determine the general location of a 911 caller by triangulating the distance from multiple cell towers to the caller's mobile device.
To implement Congress's mandate, the Federal Communications Commission (FCC) has defined cellular telephone system upgrades to be accomplished in two phases.
Phase I provides the call-taker with the ability to see the mobile device-phone number of the 9-1-1 caller and the location of the cell-tower antenna with which the mobile device is connected. This phase also requires that the call be routed to the PSAP nearest to that tower. As of 2006, 83.6 percent of PSAPs have met all or part of Phase I requirements. Using the cell-tower location, Phase I technology can only locate a mobile device within a 3-6 mile radius.
Phase II provides the call-taker with the ability to see the mobile device phone number and the location of caller to an accuracy of 50 to 300 meters depending on the type of location system being used by the wireless provider. This phase also requires that the call be routed to the PSAP nearest to that location or nearest to the cell antenna in use, depending on the particulars of the system. As of 2006, 65.2 percent of PSAPs have met all or part of Phase II requirements.
There is no standardized method for implementing Phase II requirements, so wireless providers, in conjunction with local public-safety agencies, are using various technologies for providing mobile device location information to PSAPs. There are two basic approaches: handset-based and network-based.
FIG. 1C illustrates how a 911 call from a mobile device is connected to a PSAP. In a handset based embodiment, a GPS receiver built into the mobile device is utilized. When a caller 101 initiates a 911 call from a mobile device with a GPS receiver built in, the GPS receiver locates itself using satellites 110 orbiting overhead. The GPS receiver in the mobile device receives radio signals emitted by at least three satellites 110, measuring the time it took the signals to reach the receiver. Using trilateration, the GPS receiver can determines its location coordinates. The location coordinate information accompanies the voice and phone data transmitted to the base station. The base station and MTSO 111 either forwards the call to the dedicated 9-1-1 switch 102 (the same ones used by landline calls) for PSAP routing or routes the call to the nearest PSAP, depending on the routing path the wireless carrier chooses. At the PSAP 103, mapping equipment (typically the CAD equipment discussed in the previous system) converts the caller's coordinates to a street address that the call-taker can understand and provide to dispatched emergency personnel.
A network-based embodiment is different from the handset-based embodiment only in how the mobile device generates its latitude and longitude coordinates. As shown in FIG. 1D, a common implementation of network-based location-finding involves putting additional radio equipment on network base stations so that, in essence, they act something like a GPS receiver for signals received from the mobile device. When a caller dials 9-1-1 on the mobile device, the mobile device sends out radio signals to at least three of cell towers 113, and receivers in each tower times how long it takes for the signal to reach the tower. Using trilateration, the network can then estimate the location of the mobile device to within an accuracy of 100 to 300 meters. Once the network has estimated the latitude and longitude coordinates of the phone, this information is included with the voice call transmitted to the network switching station 111 via the base station 112 from which it is connected.
While local citizens using their mobile devices may now access conventional emergency call service systems, large scale emergencies sometimes destroy or render inoperable conventional emergency call service systems. For example, large scale emergencies such as natural disasters (e.g., earthquakes, floods and hurricanes) and terrorist attacks can disable some or all PSTN telephone and cellular telephone infrastructure. In such instances, citizens using either wired or wireless communication devices do not have any access to emergency call services. Cut off from 911 service, citizens are no longer able to aid first responders by reporting developments on their cell phones.